1. Field of the Invention
The present invention relates to a printing apparatus and a facsimile apparatus using the same. More particularly, the present invention relates to a printing apparatus for use in a facsimile apparatus which communicates data according to a communication system normalized for example by CCITT (International Telegraph Telephone Consultative Committee), and to a facsimile apparatus using the printing apparatus.
2. Description of the Background Art
Recently, facsimile apparatus have been widely utilized not only in offices but also in homes, and it is strongly desired to reduce the sizes and costs. Therefore, in compliance with such desire, a facsimile apparatus needs to have a simplified structure and a reduced number of components.
Meanwhile, in order to communicate image data between facsimile apparatuses of different types, communication of image data by facsimile apparatus needs to be performed according to a communication system normalized by CCITT for example. In the communication system called GIII normalized by CCITT, there are provided a standard image data communication mode called a standard mode, and a mode enabling communication of image data of high definition called a fine mode.
FIGS. 1A to 1D are diagrams for explaining image reading operation in a conventional facsimile apparatus. As shown in FIG. 1A, if a line l4 exists on an original 41, the original image is read by reading means such as a one-dimensional contact type image sensor arranged along the horizontal direction in FIG. 1A while the original 41 is being carried in the direction shown by the arrow 42. In this case, in the standard mode, an area having a width L1 is regarded as one line and reading operation is performed for each line successively. Thus, reading operation for one line is performed in the order of line l3, line l2 and line l1. A printing form of the image data thus read is shown in FIG. 1B. Referring to FIG. 1B, pixels to be used for printing are shown as the hatched areas. In the line l3, as for the pixels in the left end region in FIG. 1B, where the line l4 shown in FIG. 1A extends horizontally as a thin line, it is determined that the data represents non-printing because of a low threshold level at the time of reading the image. In addition, as for the pixels near the region between the lines l1 and l2 in the line l4 and the region between the lines l2 and l3 in the line l4, the image data represents non-printing. Accordingly, if the image of the original 41 is thus read, the image data of the line l4 is transmitted in a broken manner as shown in FIG. 1B.
FIG. 1C shows original reading operation in the fine mode. If the original 41 shown in FIG. 1A is to be read in the fine mode, reading operation is performed by regarding an area having a width L2 half of the above-mentioned width L1 as one line. Thus, reading operation for the respective lines is performed successively in the order of the lines l3b, l3a, l2b, l2a, l1b, l1a, whereby the printing form based on the read image data becomes relatively approximate to the image of the original 41 as shown in FIG. 1C. In this case, the threshold level at the time of reading the image is a level for the width L2 and even if a relatively thin line is read, the data is not determined to be non-printing. Thus, image reading in the standard mode involves a disadvantage that at the time of transmitting the image of the original 41 having a horizontal thin line for example, the horizontal thin line would disappear.
Normally, a facsimile apparatus is provided with a line type thermal head and image data transmitted from a facsimile apparatus on the other side is thermally printed on thermal printing paper by means of this line type thermal head. Such a line type thermal head includes a plurality of heating elements arranged in one line and those heating elements are selectively heated based on printing data.
FIGS. 2A and 2B are diagrams for explaining printing operation in a conventional facsimile apparatus. Particularly, FIG. 2A represents the fine mode and FIG. 2B represents the standard mode. FIGS. 3A and 3B are diagrams for explaining a smoothing process of printing operation in the facsimile apparatus.
Referring to those figures, a plurality of heating elements Tj (j=1, 2, . . . , n) are arranged horizontally in the facsimile apparatus and printing paper 44 as thermal printing paper is fed on those heating elements Tj in the direction of the arrow 43. Each of the heating elements Tj has a width L1 in the feeding direction of the printing paper 44, namely, in the direction of the arrow 43, and when printing for one line by the heating elements Tj is terminated, the printing paper 44 is fed by the width L1 in the direction of the arrow 43. Thus, in the fine mode, printing is performed based on the image data corresponding to each of the lines l1, l2 having the width L1.
In the standard mode, one line l3 has a width L2 twice larger than the width L1 as shown in FIG. 2B. Consequently, one line l3 cannot be printed by one printing operation by the heating elements Tj of the width L1 and two printing operations are performed based on the image data for one line. Thus, based on the image data for one line, printing operation for the area shown by l3b is performed first and then after the printing paper 44 is fed by the width L1, printing operation for the area shown by l3a is performed. After that, the printing paper 44 is further fed by the width L1 and printing operation for the subsequent line is performed. Such printing operations are repeated, whereby an image is printed on the printing paper 44.
However, in the case of the standard mode in which two printing operations are performed based on the same printing data, there are caused step portions between the respective lines as shown in FIG. 3A and thus it is not possible to print an image of a high definition. In FIG. 3A, the hatched area represents a printed image.
FIG. 4 is a schematic block diagram showing a conventional facsimile apparatus in which an improvement has been made in reading and printing of image data. Referring to FIG. 4, the facsimile apparatus 1 includes: an operation panel 2 provided with input key groups and so on; a reading unit 3 for reading an image of an original; a central processing circuit 8 for performing operation such as coding and decoding of image data; a printing unit 9 for printing the image on printing paper; and a transmission control circuit 10 for controlling line connection and the like. In addition, in order to enable the facsimile apparatus 1 to have a telephone function, a telephone circuit 11, a handset 12 and the like are connected to the transmission control circuit 10.
Next, description will be made of a case in which the facsimile apparatus 1 reads an original image and transmits the image in the standard mode. The reading unit 3 includes a reader 4 such as a one-dimensional contact type image sensor, an A/D converter 5, a signal processing circuit 6, and a memory 7. An original image is read by the reader 4 for each line of the same width L2 as that in the fine mode. An analog signal from the reader 4 is converted by the A/D converter 5 to binary data. The signal processing circuit 6 stores image data for one line into the memory 7 and performs signal processing such as calculation of a logical sum between the image data of the line outputted from the A/D converter 5 and the image data of the line stored in the memory 7. For example, the above-mentioned image data of the line l3b shown in FIG. 1C is stored in the memory 7 and a logical sum between this image data and the image data of the line l3a supplied next is calculated for each pixel. In consequence, by reading operation for two lines as in the fine mode, the signal processing circuit 6 outputs image data for one line. The result of the processing is outputted as binary data to the central processing circuit 8. This binary data is coded in the central processing circuit 8 and the coded data is modulated in the transmission control circuit 10, whereby it is transmitted to the telephone line T in a communication system of the standard mode.
Thus, in the facsimile apparatus 1, in order to transmit an original image in the standard mode, the original image is read for each line of the width L2 in the same manner as in reading operation in the fine mode. Signal processing in the signal processing circuit 6 is performed by calculating a logical sum for the image data in the lines l1a and l1b as shown in FIG. 1C for example. Similarly, logical sums are calculated between the lines l2a and l2b and between the lines l3a and l3b. Accordingly, the printing form based on the image data obtained after such signal processing is as shown in FIG. 1D. Thus, in the case of transmitting an image in the standard mode in the facsimile apparatus 1, even if the original 41 contains a thin line in the horizontal direction, the image data can be transmitted without causing any problem such as disappearance of the thin line.
As described above, in the case of transmitting an original image in the standard mode in the conventional facsimile apparatus 1, the special memory 7 is required as a storage area for applying the above-mentioned signal processing to the image data read by the reader 4, which causes disadvantages such as a high cost and a large size of the apparatus. In addition, at the time of transmitting image data, the telephone line T is connected for the transmission of the image data and it can not receive image data from other facsimile apparatus, making it impossible to use the printing unit 9. Thus, at the time of transmitting image data, the printing unit 9 is not used and thus the structure involves a loss, causing deterioration of the efficiency of use of the facsimile apparatus 1.
Next, printing operation in the facsimile apparatus 1 shown in FIG. 4 will be described. The printing unit 9 includes: a drive circuit 91; a pulse motor 92 driven by the driver circuit 91 for feeding the printing paper; a printing data correcting circuit 93 for correcting printing data supplied from the central processing circuit 8 and supplying the corrected printing data; a memory 94 for storing the printing data supplied from the printing data correcting circuit 93; and a printing head 95. In the standard mode, the central processing circuit 8 supplies binary data of one line for two printing operations. The printing data correcting circuit 93 makes a correction of the printing data supplied from the central processing circuit 9, referring to printing data stored in the memory 94. Consequently, the printing data correcting circuit 93 supplies different printing data for each printing operation. The printing head 95 includes a plurality of printing elements T1 to Tn, and a shift register R having cells Ri corresponding to the respective printing elements Ti (i=1, 2, . . . , n). The printing data supplied from the printing data correcting circuit 93 is supplied to the shift register R and the printing data for one printing operation is stored in the cells R1 to Rn. The heating elements Ti are selectively heated based on the data stored in the cells Ri, so that one printing operation is performed. After that, the central processing circuit 8 controls the pulse motor 92 through the drive circuit 91, so that the printing paper 44 is fed by the width L1 and the subsequent printing operation is performed.
In the above-described facsimile apparatus 1, the printing data correcting circuit 93 and the memory 94 are provided and even if image data is transmitted in the standard mode, smoothing processing is applied to the printing data and pixels 45, 46 as shown in FIG. 3A are printed. Accordingly, the printing form is as shown in FIG. 3B and a boundary between the non-printing area and the printing area for example becomes smooth. Thus, it is possible to print an image of a relatively high definition.
However, in the above-described facsimile apparatus, the printing data correcting circuit 93 refers to the already supplied printing data and thus the dedicated memory 94 is required, which causes the apparatus to be expensive and makes it difficult to reduce the size of the apparatus.